System and method for providing a control signal

ABSTRACT

The system, which provides a control signal, includes an over-current control unit, a time clock that provides a periodic time signal, and a clock generator unit that includes a first input terminal, a second input terminal, and an output terminal. The first input terminal is coupled to the time clock and the output terminal is coupled to the over-current control unit. The first input terminal of the clock generator unit receives the periodic time signal and the second input terminal of the clock generator unit receives a modification signal. The clock generator unit generates a clock signal based on the periodic time signal and the modification signal. The output terminal of the clock generator unit provides the clock signal to the over-current control unit, and the over-current control unit provides a control signal based on the clock signal.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the field of providing a controlsignal, in particular a control signal for controlling a load, forexample a bulb. In particular, the present invention relates to a systemfor providing a control signal. Further, the present invention relatesto a method of providing a control signal. Moreover, the inventionrelates to a program element. Furthermore, the invention relates to acomputer-readable medium.

Further, this invention discloses in particular a method for driving abulb, in particular an incandescent bulb, by a semiconductor switch.Thereby, the drive strategy allows to control the energy provided to thebulb as well as the switch in order to minimize the stress inside thesemiconductor switch in case of overload conditions.

Integrated smart power switches use different protection strategies toprevent the switch from destruction during overload conditions.

The most common strategy is to apply an over-temperature shutdown, whichprotects the switch in case of a high power dissipation especially athigh ambient temperatures. The disadvantage of this solution is apossible high permanent junction temperature which degrades and finallydestroys the semiconductor switch.

An improved protection strategy is to use a linear current limitationwhich limits the switch current to values which are not critical to theswitch. The main drawback is this strategy introduces a high amount ofpower dissipation in the switch during the turn-on phase of a capacitiveload or an incandescent bulb. Therefore, the switch must be deactivatedby a supervising intelligence in case of overload, e.g. outputshort-circuit, to prevent it from destruction.

Other components use a multilevel over-current shutdown strategydependant on the load type. Thereby, the switch is deactivatedimmediately in case of an overload condition in order to protect it fromdestruction. This strategy suffers from an uncertainty of the warm uptime due to

-   -   a pulse width modulated operation (PWM), e.g. during power        control or theatre dimming or    -   an initialisation phase of an intelligent load ballast which        causes a delay time until switch on of the load.

In this case, either the time-window of the current has to be enlargedwhich is a risk for the switch in case of over load or the over-currentshutdown threshold of the switch is triggered, because the load has notyet reached the operating temperature.

This is described in more detail along with the following FIGS. 1, 2, 6,7 and 8.

FIG. 1 shows schematically a common circuit 1 in order to generate amultilevel over-current shutdown strategy inside a smart power switch.The circuit 1 includes an output driver 10, a pulse widthmodulation—controller (PWM-controller) 11, an over-current control 12, abulb or High Intensity Discharge (HID) ballast 13, a time clock 14 and acontroller 15. The controller 15 determines which duty cycle thePWM-controller 11 is applying to a signal. The over-current control 12is triggered by the controller command 15 and the time clock 14. Withthe ON/OFF command a timer is started inside the over-current control12. This over-current control 12 counts the inrush phase and enables theproper threshold of the over-current shutdown to switch on anincandescent bulb.

FIG. 2 shows schematically a diagram of the inrush current 20, which isplotted at the vertical axis, of an incandescent bulb driven with theexample of a two-step over-current shutdown strategy with regard to theelapsing time t. The controller 15 triggers continuously an on-command21 to the over-current control 12.

The over-current thresholds and time-windows are adjusted according tothe maximum load condition in order to securely start the device underall operating conditions, e.g. voltage, ambient temperature andtolerances.

During high over-current threshold phases the switch can be potentiallystressed in case of an over load condition e.g. short circuit which cannot be distinguished from a bulb turn-on condition.

For new applications the switch has to be operated in PWM mode in orderto limit the operating voltage and to provide a dimming or a soft start,e.g. for theatre dimming. But the PWM is limiting the root mean squarevoltage at the bulb and thereby enlarges the time until the bulb currentdrops below the DC over-current threshold.

To overcome this issue there are 2 common strategies in order to handlethe PWM operation:

-   -   1. Use of a huge chip area in order to enable the switch to        handle the high energy amount during a long time-window. The        disadvantage is the high cost for a huge chip area.    -   2. The bulb is generally started with a constant on pulse until        the bulb is warm enough to drop under the DC over current        threshold. The drawbacks of this constant on pulse are, that the        pulse time has to be controlled by the supervising intelligence        which requires calculating time and also may cause a light flash        when not set properly especially at low duty cycles.

FIG. 6 shows a schematic diagram of an inrush current 22 with a dutycycle less than 1. In this case, using a common circuit, would lead toan over current shutdown as the inrush current may be higher than anover current control cycle when a duty cycle of less than 1 is used.When the window time is too short, the inrush current would reach theover current control threshold and an over current shutdown would occur.Therefore, it may be necessary to adapt the window time of the overcurrent control.

FIG. 7 shows a schematic diagram of an inrush current 20 of a xenonload, which is plotted at the vertical axis with regard to the elapsingtime t. The first peak in the current flow shows the charging currentinto the input capacitances of a component. A specific time period afterturning on, the load is kept in a so called “power on reset” state. Forobtaining a stable turning on behaviour, the load is supplied with powerduring this time whilst the normal mode, that means for example anillumination, is prevented internally. After the expiration of this timeperiod, there is a further current pulse, illustrated by the second peakin FIG. 6, caused by the change to the normal mode. The time between thepulses or peaks is dependent on tolerances of the load and dependent onthe respective producer.

The current thresholds and window times of the inrush current has to bedimensioned for a maximum “power on reset” time in order to start theload under all operating conditions, like voltage, ambient temperature,tolerances. If the window time is too short, the load current reachesthe shutdown threshold leading to an immediate shutdown of the switch.This may be seen in FIG. 8. On the other hand, an extension of thewindow times would lead, in the case of an overload just under theshutdown threshold, to a high stress causing a failure of the component.

BRIEF SUMMARY OF THE INVENTION

A problem to be solved by the present invention is therefore, to providea system and a method which may overcome the disadvantages of the stateof the art.

This problem may be solved by a system and a method according to theindependent claims. Preferred embodiments, which can be used alone or incombination with each other, are presented in the dependent claims.

According to a first aspect of the invention, a system is provided forproviding a control signal for controlling a load, for example a bulb,wherein the system comprises an over-current control, a time clock,which is adapted to provide a periodical time signal, and a clockgenerator unit comprising a first input terminal and a second inputterminal and an output terminal, wherein the first input terminal iscoupled to the time clock and the output terminal is coupled to theover-current control, the clock generator unit being adapted to receivethe periodical time signal at the first input terminal and to receive amodification signal at the second input terminal and wherein the clockgenerator unit is adapted to generate a clock signal on the basis of theperiodical time signal and the modification signal and wherein the clockgenerator unit is further adapted to provide the clock signal to theover-current control at the output terminal, wherein the over-currentcontrol is adapted to provide a control signal on the basis of the clocksignal.

The over current control may generate a control signal or over currentcontrol signal on the basis of the clock signal generated by the clockgenerator circuit. The time clock may be any kind of device or unitproviding a periodical time signal.

With this system, the length of the inrush current windows may beadapted to the turning on profile of the used load, for example a bulbload. This is possible as the time counter is proceeding only when theload is turned on and thereby is warmed up.

According to a second aspect of the invention, a method of providing acontrol signal is provided, wherein the method comprises providing aperiodical time signal by a time clock, receiving the periodical timesignal at a first input terminal of a clock generator unit, receiving amodification signal at a second input terminal of the clock generatorunit, generating a clock signal on the basis of the periodical timesignal and the modification signal, providing the clock signal to anover-current control at the output terminal of the clock generator unit,providing a control signal on the basis of the clock signal by theover-current control.

According to a further aspect of the invention, a computer-readablemedium (for instance a semiconductor memory, a CD, a DVD, a USB stick, afloppy disk or a harddisk) is provided, in which a computer program ofproviding a clock signal is stored, which computer program, when beingexecuted by a processor, is adapted to carry out or control a method ofproviding a clock signal having the above mentioned features.

According to a further aspect of the invention, a program element (forinstance a software routine, in source code or in executable code) ofproviding a clock signal is provided, which program element, when beingexecuted by a processor, is adapted to carry out or control a method ofproviding a clock signal having the above mentioned features.

Providing a clock signal, which may be performed according toembodiments of the invention, can be realized by a computer program,that is by software, or by using one or more special electronicoptimization circuits, that is in hardware, or in hybrid form, that isby means of software components and hardware components.

According to an exemplary embodiment, the control signal corresponds toa current-threshold value. The current-threshold value may be dependenton the maximum load conditions in order to securely start the device orload under all operating conditions.

According to a further exemplary embodiment, the system furthercomprises an output driver coupled to the over-current control forproviding current pulses to a load on the basis of the control signal. Abulb for example may be generally started with a constant on pulse untilthe bulb is warm enough to drop under the DC over current threshold.

According to a further exemplary embodiment, the system furthercomprises a pulse width modulation controller coupled to an inputterminal of the output driver and being adapted to provide signal-pulseswith a certain, predetermined duty cycle to the output driver. Theoutput driver may then generate an output signal based on these pulsessupplied to the load.

According to a further exemplary embodiment, the output driver comprisesa switch, the switch being adapted to provide the current pulses to theload in a first position, wherein the first position is set if a valueof the current pulses resulting from the signal-pulses of the pulsewidth modulation controller is below a current-threshold value of theover-current controller.

According to a further exemplary embodiment, the load is a bulb, inparticular an incandescent bulb.

According to a further exemplary embodiment, the clock generator unitcomprises an AND-Gate having a first input and a second input where thefirst input is connected to the pulse width modulation controller andthe second input is connected to the time clock; and an output beingadapted to provide an outgoing signal combining the signals received bythe first and the second input in order to synchronise the signals ofthe time clock with the signals of the pulse width modulationcontroller, so that it is ensured that the bulb is turned on and theswitch is not destroyed in case of an overload. In this embodiment, thesignal resulting from the pulse width modulation controller may be themodification signal.

According to a further exemplary embodiment, the second input terminalof the clock generator is coupled to an output terminal of the outputdriver, wherein the output driver is adapted to provide a feedbacksignal from the output driver to the clock generator unit. The feedbacksignal may generate an open load signal. This signal may indicate if acurrent flows or not. If an ignition of an automotive is activated, theopen load signal may be switched off. The feedback signal may be themodification signal and may be used to generate the clock signal.

According to a further exemplary embodiment, the clock generator unitcomprises a switch being responsive to the feedback signal. The switchmay be affected when the feedback signal, for example the open loadsignal, changes. The feedback signal may change for example between twostates.

According to a further exemplary embodiment, the clock generator unit isadapted to provide as clock signal in a first operating state theperiodical time signal and in a second operating state a modifiedperiodical time signal. This may denote that the periodical time signalis directly supplied to the over current control in the first operatingstate and indirectly via a modification unit in the second operatingstate.

According to a further exemplary embodiment, the modified periodicaltime signal is the periodical time signal divided by n. n may be anyinteger. With this embodiment, it may be possible that the clockfrequency of the clock signal generated in the clock generator unit maybe reduced. Therefore, the time period of the over current windows maybe increased, since the same is deferred by a given number of clockcylces.

According to a further exemplary embodiment, the switch is adapted toswitch the clock generator unit between the first and the secondoperating state. The switch may be a transistor, in particular afield-effect transistor. Switching between the both operating states maybe carried out in response to the open load signal.

The invention provides further an apparatus procedure to adopt theinrush current of incandescent bulbs by using the fact that the bulb isonly warmed up during on-time of the switch. Thereby the time counterwhich controls the inrush phase is gated with the on-signal of theswitch.

In another aspect, the invention inhibits further an apparatus tocontrol a bulb, in particular an incandescent bulb, by a smart switchincluding

-   -   a bulb,    -   an over-current control which provides a current-threshold value        to an output driver,    -   a pulse width modulation controller which provides signal-pulses        with a certain duty cycle to the output driver,    -   an output driver for providing current pulses to the bulb, the        output driver comprising a switch having a first position in        which the current-pulses are provided to the bulb, wherein the        first position is set if the current pulses resulting from the        signal-pulses of the pulse width modulation controller are below        the current-threshold value of the over-current controller,    -   a time clock which provides a periodical time signal with a        certain length, whereas    -   an AND-Gate having a first input and a second input where the        first input is connected to the pulse width modulation        controller and the second input is connected to the time clock;        and an output providing an outgoing signal combining the signals        received by the first and the second input in order to        synchronise the signals of the time clock with the signals of        the pulse width modulation controller, so that it is ensured        that the bulb is turned on and the switch is not destroyed in        case of an overload.

In another aspect the invention is about a method to use the apparatusof the previous paragraph, where the timers in the over-current controlare incremented only during the on-phase of the PWM-values in order tomatch the over-current window to different PWM-signals.

This may enlarge the time of the switch on phase but may not increasethe maximum energy in the switch because only the on phases represent arisk for the switch.

Due to the thermal inertia of the bulbs there may be only a low coolingeffect inside the bulb during switch off phase.

As a consequence the switch may be designed with a low chip area as in acommon design but also survives low duty cycle operation without risk orlight flashes.

Further details and advantages of the invention are explained withregard to the enclosed figures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a schematic diagram of a common circuit;

FIG. 2 shows a schematic diagram of an inrush current;

FIG. 3 shows a circuit 2 in order to generate a multilevel over-currentshutdown;

FIG. 4 shows schematically a diagram of the inrush current 22 with aduty cycle of 1;

FIG. 5 shows schematically a diagram of the inrush current 22 with aduty cycle not 1;

FIG. 6 shows schematically a diagram of the inrush current with a dutycycle less than 1;

FIG. 7 shows a schematic diagram of the inrush current of a xenon load;

FIG. 8 shows a schematic diagram of the inrush current with shutdown;

FIG. 9 shows a schematic block diagram of a system according to anembodiment of the application;

FIG. 10 shows a schematic inrush current and a modified inrush windowaccording to an embodiment of the application;

FIG. 11 shows a schematic inrush current with a over current shutdownaccording to an embodiment of the application;

FIG. 12 shows a block diagram of a system according to an embodiment ofthe invention.

DESCRIPTION OF THE INVENTION

With regard to the following description of the embodiments of theinvention the same reference signs refer to the same or comparablecomponents.

FIG. 3 shows a first embodiment according to the application comprisinga circuit 2 in order to generate a multilevel over-current shutdownstrategy inside a smart power switch. The circuit 2 includes an outputdriver 10, a pulse width modulation-controller (PWM-controller) 11, anover-current control 12, a bulb 13, a time clock 14 and a controller 15.The controller 15 determines which duty cycle the PWM-controller 11 isapplying to a signal. The over-current control 12 is receiving thesignal of an AND-Gate 16 which has two inputs, one input by the pulsewidth modulation controller the other by the time clock 14.

Additionally, a controller 15 is sending its signals to the over-currentcontrol 12. With the ON/OFF command a timer is started inside theover-current control 12. This over-current control 12 counts the inrushphase and enables the proper threshold of the over-current shutdown toswitch on an incandescent bulb. This enlarges the time of the switch onphase but does not increase the maximum energy in the switch becauseonly the on phases represent a risk for the switch. The circuit 2further includes a logical AND-Gate 16 in order to synchronise thePWM-controller 11 and the time clock 14 before entering the signal intothe over-current control 12.

Due to the thermal inertia of the bulbs there is only a low coolingeffect inside the bulb during switch off phase. Therefore, the inrushtime can be enlarged inverse proportional to the duty cycle with a verygood approximation:

$T = \frac{T\left( {100\%} \right)}{d.c.}$

FIG. 4 shows schematically a diagram of the inrush current 22, which isplotted at the vertical axis, of an incandescent bulb with regard to theelapsing time t. The difference to FIG. 2 gets visible, when a PWMoperation is applied. Thereby, the over current windows are onlyproceeding, when the switch is in on phase.

FIG. 5 shows schematically a diagram of the inrush current 22, which isplotted at the vertical axis, of an incandescent bulb with regard to theelapsing time t. The difference to FIG. 2 gets visible, when a PWMoperation is applied. Thereby the windows are only proceeding, when theswitch is in on phase.

The area W under the over-current windows which refer to the max. energyin case of over load is constant independent on the PWM duty cycle.W=I ² ·R _(DSON) ·T ₁

-   -   I=over current threshold    -   R_(DSON)=On resistance of the switch    -   d.c.=duty cycle

As a consequence the switch can be designed with a low chip area as in acommon design but also survives low duty cycle operation without anyrisk in case of over load or light flashes in case of low duty cycles.

The present invention may be of particular use for the control of bulbsin vehicles.

FIG. 9 shows a second embodiment of the system according to theapplication. The system 2 comprises a control unit or SPI register 15coupled to a pulse width modulation (PWM) modulator 11. The PWMmodulator 11 supplies a signal to an output driver 10. An outputterminal of the output driver 10 is coupled to an HID ballast. Thecontrol unit 15 supplies an on/off-signal to an over current controlunit 12, when the load is turned on. The over current control thenprovides a control signal to the output driver 10. The load is thereforecontrolled by the output driver in correspondence to the control signalprovided by the over current control unit 12.

The over current control generates an over current control signal on thebasis of a clock signal. This clock signal is provided by a clockgenerator unit. The clock generator unit comprises two input terminalsand an output terminal. The output terminal is coupled to the overcurrent control unit 12 for providing a clock signal. The clockgenerator unit is coupled with a first input terminal to a time clock14. The time clock provides a periodical time signal. In a firstoperating state, the clock signal generated by the clock generator unitis equal to the periodical time signal.

The clock generator unit comprises further a switch 18. The switch 18 isresponsive to a modification or open load signal 19 provided by afeedback signal from the output driver 10. If the modification signal ison, the clock generator unit is switched by the switch 18 to a secondoperating state. In this second operating state, the periodical timesignal is divided by n (block 17) before being supplied to the overcurrent control 12. n may be any specified value, in particular aninteger number.

With this system, the length of the inrush current windows may beadapted to the turning on profile of the used xenon load. This ispossible as the load only needs a small current in its power on resetmode.

The control unit 15 controls the load over the PWM modulator 11 and theoutput driver 10. When the load 13 is turned on, the over currentcontrol unit 12 receives the on-signal from the control unit 15 and thenstarts a counter with the received clock signal. At given counterreadings, the shutdown threshold is set to a next value or step. Theoutput driver 10 measures the output current and deactivates the output,if the shutdown threshold given by the over current control unit 12 isexceeded. During the power on reset mode of the load, the output driver10 recognizes that there exist only a small load current and generates asignal “open load”. This signal is sent as feedback signal to the clockgenerator unit. If the current is lower than the open load threshold,the clock of the counter is divided by n for the shutdown threshold andthe expiration of the windows of the current thresholds is thereforedecreased.

The system 2 supports the method of controlling a xenon lamp withintelligent semiconductor switch with a multilevel over currentshutdown. The time periods of the over current shutdown windows may beincreased in the case of a delayed starting of the load. The increasingof the time periods may be carried out by a reduction of the clockfrequency of the respective counter. The increasing of the time periodsmay be further carried out by an interruption of the clock frequency ofthe respective counter. The reduction of the clock frequency may becarried out by a frequency divider. A discrete control signal maycontrol the delayed starting of the load. Deceeding a current thresholdmay be detected as a delayed starting of the load. The increasing of thetime periods of the over current shutdown windows may be carried out foronly a part of the windows. The increasing of the time periods may beswitched off and on in the semiconductor switch.

FIG. 10 shows a schematic diagram of an inrush current and a modifiedinrush window according to an embodiment of the application. Caused bythe open load signal, the frequency of the clock signal is reduced andthe first inrush current window is therefore extended. Thus, the overcurrent shutdown will not be activated at the second pulse of the loadcurrent.

In the case of an overload, the power loss and the stress of thecomponent will not be increased. This may be seen in FIG. 11. Switchingthe counter for the over current shutdown to a slower clock frequencymay be prohibited for specific levels, for example high currentthresholds, which are not necessary for controlling a xenon load. Thus,the stress influencing the component in a failure situation may befurther reduced.

Further, it would also be possible to stop the clock for the countercompletely during the open load time period.

FIG. 12 shows a system combining the systems of FIGS. 3 and 9. Thesystem comprises the components of the system according to FIG. 9. Thesystem 2 further comprises an AND gate 16 in the direct path from thetime clock 14 to the over current control unit 12. A first inputterminal of the AND gate 16 is coupled to the output of the PWMmodulator 11. A second input terminal of the AND gate 16 is coupled tothe output of the time clock. The output terminal of the AND gate 16 iscoupled to the input terminal of the over current control unit 12.

When the clock generator unit is in the first operating state, thatmeans that the periodical time signal is not divided by n, the clocksignal generated by the clock generator unit corresponds to the clocksignal generated in the system of FIG. 3.

This system may therefore provide the advantages of the systems of FIGS.3 and 9 in combination.

It should be noted that the term “comprising” does not exclude otherelements or features and the “a” or “an” does not exclude a plurality.Also elements described in association with different embodiments may becombined.

It should also be noted that reference signs in the claims shall not beconstrued as limiting the scope of the claims.

The invention claimed is:
 1. A system for providing a control signal,the system comprising: an over-current control unit; a time clockproviding a periodic time signal; and a clock generator unit including afirst input terminal coupled to said time clock to receive the periodictime signal, a second input terminal receiving a modification signal,and an output terminal coupled to said over-current control unit; saidclock generator unit generating a clock signal based on the periodictime signal and the modification signal; said output terminal of saidclock generator unit providing the clock signal to said over-currentcontrol unit; and said over-current control unit providing a controlsignal based on the clock signal.
 2. The system according to claim 1,wherein the control signal corresponds to a current-threshold valuedependent on a maximum load condition.
 3. The system according to claim1, comprising: an output driver coupled to said over-current controlunit, said output driver providing current pulses to a load based on thecontrol signal.
 4. The system according to claim 3, comprising: a pulsewidth modulation controller; said output driver including an inputterminal coupled to said pulse width modulation controller; said pulsewidth modulation controller providing signal-pulses with a predeterminedduty cycle to said output driver.
 5. The system according to claim 4,wherein: said output driver includes a switch having a first position inwhich the current pulses are provided to the load; and said switch isset to said first position if a value of current pulses resulting fromthe signal pulses of said pulse width modulation controller is below acurrent-threshold value of said over-current control unit.
 6. The systemaccording to claim 3, wherein the load is a bulb.
 7. The systemaccording to claim 4, wherein: the load is a bulb; said clock generatorunit includes an AND-Gate with a first input that is connected to saidpulse width modulation controller and a second input that is connectedto said time clock; and said clock generator unit includes an outputproviding an output signal that combines the signal-pulses of said pulsewidth modulation controller that are received by said first input ofsaid AND-Gate and the periodic time signal of said time clock that isreceived by said second input of said AND-Gate in order to synchronizethe periodic time signal of said time clock with the signal-pulses ofsaid pulse width modulation controller to ensure that the bulb is turnedon and said switch is not destroyed in case of an overload.
 8. Thesystem according to claim 3, wherein: said output driver includes anoutput terminal that is coupled to said second input terminal of saidclock generator unit; and said output driver provides a feedback signalto said clock generator unit.
 9. The system according to claim 8,wherein: said clock generator unit includes a switch responsive to thefeedback signal.
 10. The system according to claim 8, wherein: saidclock generator unit has a first operating state in which said clockgenerator unit provides the periodic time signal as the clock signal;and said clock generator unit has a second operating state in which saidclock generator unit provides a modified periodic time signal as theclock signal.
 11. The system according to claim 10, wherein the modifiedperiodic time signal is the periodic time signal divided by n, and n isan integer greater than
 1. 12. The system according to claim 10,wherein: said switch switches said clock generator unit between thefirst operating state and the second operating state.
 13. The systemaccording to claim 3, wherein the load is an incandescent bulb.
 14. Thesystem according to claim 1, wherein said clock generator unit has anoperating mode in which the clock signal generated by said clockgenerator unit is the periodic time signal provided by said time clock.15. A method for providing a control signal, the method which comprises:providing a periodic time signal from a time clock; receiving theperiodic time signal at a first input terminal of a clock generatorunit, and receiving a modification signal at a second input terminal ofthe clock generator unit; generating a clock signal based on theperiodic time signal and the modification signal; providing the clocksignal from an output terminal of the clock generator unit to anover-current control unit; and providing a control signal from theover-current control unit based on the clock signal.
 16. The methodaccording to claim 15, wherein the control signal provided by theover-current control unit corresponds to a current-threshold valuedependent on a maximum load condition.
 17. The method according to claim15, which comprises providing an operating mode in which the clocksignal from the output terminal of the clock generator unit is theperiodic time signal provided by the time clock.
 18. A non-transitorycomputer-readable medium comprising: a computer program stored on thenon-transitory computer-readable medium, the computer program, whenexecuted by a processor, carrying out or controlling a method including:providing a periodic time signal from a time clock; receiving theperiodic time signal at a first input terminal of a clock generatorunit, and receiving a modification signal at a second input terminal ofthe clock generator unit; generating a clock signal based on theperiodic time signal and the modification signal; providing the clocksignal from an output terminal of the clock generator unit to anover-current control unit; and providing a control signal from theover-current control unit based on the clock signal.